In U.S. Pat. No. 5,934,384, a shaft 1, a stop 2, a C-clip 3, a spring 4, a ring 5, a chuck 6, a magnet 7 and a bit 8 are disclosed (FIG. 2). The shaft 1 includes a polygonal hole 10 in an end, an annular grove 11 in the periphery, an aperture 110 communicating the polygonal hole 10 with the annular groove 11, an annular groove 12 in the periphery and a polygonal rod 13 at an opposite end. The stop 2 includes a rod 20 extending from a central portion. The stop 2 is put in the annular groove 11 so that the rod 20 can be inserted into the polygonal hole 10 through the aperture 110. The C-clip 3 is put in the annular groove 12. The magnet 7 is fit in the polygonal hole 10. The chuck 6 includes a tapered orifice 61. The chuck 6 is put around the shaft 1. The spring 4 is put around the shaft 1 and in the chuck 6. The ring 5 is put around the shaft 1 and fit in the chuck 6. Thus, the chuck 6 is kept around the shaft 1. Due to the spring 4 compressed between the C-clip 3 and the ring 5, the chuck 6 is biased in a direction so that the tapered orifice 61 pushes the stop 2 so as to insert the rod 20 into the polygonal hole 10 (FIG. 4). The bit 8 includes a polygonal shank 80 that includes several corners 81 each defining a cut 82. The chuck 6 can be moved in an opposite direction so that the tapered orifice 61 releases the stop 2 so as to allow the rod 20 to leave the polygonal hole 10 (FIG. 6). Thus, the bit 8 can be inserted in the polygonal hole 10. The chuck 6 can be released so that the rod 20 is inserted into one of the cuts 82. Thus, the bit 8 is kept on the shaft 1. The rod 20 is however inadequate to keep the bit 8 on the shaft 1. When this happens during operation, the bit 8 might cause human casualty.
There have been devised various hand tools that each include a bit engaged with a handle in a releasable manner. Generally, such a bit includes an insert, and such a handle includes a socket for receiving the insert. A locking device is used to lock the insert in the socket.